Many people die yearly from sudden cardiac death. In the vast majority of these cases, the cause of death is ventricular tachycardia and/or ventricular fibrillation. Automatic implantable cardioverting/defibrillating devices have been developed and shown to be effective in preventing sudden cardiac death from these causes.
Cardioversion (performed by a cardioverter) may be defined as the correction of either ventricular tachycardia or ventricular fibrillation by the discharge of electrical energy (e.g., shock) into the heart. The shock may be either synchronized or non-synchronized. Ventricular tachycardia is an abnormally rapid heart rate (120-240 beats per minute) originating in the heart's main pumping chambers (ventricles) which is regular in periodicity and often is life threatening to the patient. Ventricular fibrillation is generally a more rapid heartbeat disorder, disorganized and irregular, or non-periodic, and is often fatal unless corrected within minutes by the discharge of electrical energy through the heart. Sometimes, cardioversion may include delivery of an electric shock to the heart to correct ventricular tachycardia. Defibrillation may likewise include the non-synchronized delivery of electrical energy to the heart to correct ventricular fibrillation.
A plurality of different types of implantable cardioverter defibrillation (ICD) systems are known in the art. For example, see each of U.S. Pat. Nos. 4,030,509; 4,662,377; 5,133,365; and 6,067,471; the disclosures of which are all hereby incorporated herein by reference. ICD systems may be used to provide electric shock to the heart in order to correct ventricular fibrillation. FIG. 1 illustrates an internal lead 3 of a conventional ICD system placed in the right ventricle 5 of a patient's heart 4. The distal tip electrode 6 is located in the right ventricular apex 7. Labeled boxes in the figure illustrate the directions in which blood is pumped throughout the body by the heart. Additional details of the FIG. 1 system are described in the aforesaid '365 patent.
Unfortunately, use of ICD systems may often be painful to the patient to which the shock is applied. A reason for this is that defibrillation shocks often extend beyond the heart and activate extracardiac muscle(s) and/or nerve tissue(s) within the peripheral chest area(s). Excessive pain is not desirable.
It will thus be apparent to those skilled in the art that there exist a need for an ICD system and/or method that may be less painful to a patient than one or more conventional ICD systems and/or methods.